cxl: Remove the CXL_DECODER_MIXED mistake

CXL_DECODER_MIXED is a safety mechanism introduced for the case where
platform firmware has programmed an endpoint decoder that straddles a
DPA partition boundary. While the kernel is careful to only allocate DPA
capacity within a single partition there is no guarantee that platform
firmware, or anything that touched the device before the current kernel,
gets that right.

However, __cxl_dpa_reserve() will never get to the CXL_DECODER_MIXED
designation because of the way it tracks partition boundaries. A
request_resource() that spans ->ram_res and ->pmem_res fails with the
following signature:

    __cxl_dpa_reserve: cxl_port endpoint15: decoder15.0: failed to reserve allocation

CXL_DECODER_MIXED is dead defensive programming after the driver has
already given up on the device. It has never offered any protection in
practice, just delete it.

Reviewed-by: Ira Weiny <[email protected]>
Reviewed-by: Jonathan Cameron <[email protected]>
Reviewed-by: Alejandro Lucero <[email protected]>
Reviewed-by: Dave Jiang <[email protected]>
Signed-off-by: Dan Williams <[email protected]>
Reviewed-by: Fan Ni <[email protected]>
Tested-by: Alejandro Lucero <[email protected]>
Link: https://patch.msgid.link/173864304660.668823.17000888505587850279.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dave Jiang <[email protected]>

Author: djbw

drivers/cxl/core/hdm.c

@@ -332,9 +332,9 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
 	else if (resource_contains(&cxlds->ram_res, res))
 		cxled->mode = CXL_DECODER_RAM;
 	else {
-		dev_warn(dev, "decoder%d.%d: %pr mixed mode not supported\n",
-			 port->id, cxled->cxld.id, cxled->dpa_res);
-		cxled->mode = CXL_DECODER_MIXED;
+		dev_warn(dev, "decoder%d.%d: %pr does not map any partition\n",
+			 port->id, cxled->cxld.id, res);
+		cxled->mode = CXL_DECODER_NONE;
 	}
 
 	port->hdm_end++;

drivers/cxl/core/region.c

@@ -2738,18 +2738,6 @@ static int poison_by_decoder(struct device *dev, void *arg)
 	if (!cxled->dpa_res || !resource_size(cxled->dpa_res))
 		return rc;
 
-	/*
-	 * Regions are only created with single mode decoders: pmem or ram.
-	 * Linux does not support mixed mode decoders. This means that
-	 * reading poison per endpoint decoder adheres to the requirement
-	 * that poison reads of pmem and ram must be separated.
-	 * CXL 3.0 Spec 8.2.9.8.4.1
-	 */
-	if (cxled->mode == CXL_DECODER_MIXED) {
-		dev_dbg(dev, "poison list read unsupported in mixed mode\n");
-		return rc;
-	}
-
 	cxlmd = cxled_to_memdev(cxled);
 	if (cxled->skip) {
 		offset = cxled->dpa_res->start - cxled->skip;

drivers/cxl/cxl.h

@@ -380,7 +380,6 @@ enum cxl_decoder_mode {
 	CXL_DECODER_NONE,
 	CXL_DECODER_RAM,
 	CXL_DECODER_PMEM,
-	CXL_DECODER_MIXED,
 	CXL_DECODER_DEAD,
 };
 
@@ -390,10 +389,9 @@ static inline const char *cxl_decoder_mode_name(enum cxl_decoder_mode mode)
 		[CXL_DECODER_NONE] = "none",
 		[CXL_DECODER_RAM] = "ram",
 		[CXL_DECODER_PMEM] = "pmem",
-		[CXL_DECODER_MIXED] = "mixed",
 	};
 
-	if (mode >= CXL_DECODER_NONE && mode <= CXL_DECODER_MIXED)
+	if (mode >= CXL_DECODER_NONE && mode < CXL_DECODER_DEAD)
 		return names[mode];
 	return "mixed";
 }